The present invention relates to a charge control type ink jet printer and, more particularly, to a device for detecting charging of ink droplets which are ejected from an ink jet head of the printer.
In an ink jet printer of the type described, it is a usual practice to check whether ink droplets, or drops, have been charged and whether charged droplets have been properly deflected. For this purpose, use is made of a charge detection device in which an integration circuit integrates a voltage which is induced in a charge detecting electrode when a charged droplet flies in the close vicinity of the electrode, or one in which an integration circuit integrates a charge of a charged droplet upon impingement of the charged droplet on a charge detecting electrode. For detecting the charged/uncharged condition only, the charge detecting electrode is located in a position where it will detect charged droplets among drops which have been applied with charging voltages under a predetermined condition. For the detection of amounts of deflection of charged droplets, on the other hand, the charge detecting electrode is so shaped and arranged as to detect charged droplets which fly a specific deflection path, instead of simply detecting charged droplets.
The prior art charged ink droplet detector which employs a charging electrode and an integration circuit as described above is usable for a phase search adapted to properly predetermine a timing for applying a charging voltage relative to a timing for generating a droplet, and for adequately setting an amount of deflection of a charged droplet (see, for example, Japanese Patent Application Nos. 53-1411836/1978, 53-164851/1978, 55-24303/1980 and 55-48882/1980).
In an ink jet printer, it is preferable to provide various notifications in response to charge detection concerning, for example, droplet charged/uncharged, phase search required/unrequired (search amid/ended), and deflection proper/improper (deflection control amid/ended). Such notifications are generally implemented by visible display elements such as light emitting diodes and/or audible elements such as buzzers or the like. Such notifications are effected by a line which is independent of the control line associated with charged drop detection, e.g. a microcomputer or a logic circuit. It is sometimes practiced to use a single computer for both the control over the charged droplet detector and that over the notifying device. In any case, the charged droplet detector and the notifying device are controlled independently of each other and by independent control signal lines, resulting in a prohibitive number of control lines and, thereby, addition of numerous circuit elements.